The objective is to define and characterize the reactions of aliphatic diazonium salts with metalloproteins. As transient intermediates in alkylation reactions, aliphatic diazonium ions are considered to be the ultimate carcinogens formed from compounds containing the nitrogen-nitrogen bond. However, arenediazonium salts undergo electron transfer with certain hemoproteins resulting in their conversion to Sigma-aryliron(III) complexes of protoporphyrin IX, and similar transformations are expected with their aliphatic counterparts. Diazonium salts will be generated in situ from diazo compounds by protonation and from N-nitrosoureas known to form diazonium salts by hydrolysis. Detailed kinetic and product analyses for reactions between diazo compounds and hemoglobin will be undertaken to establish the stoichiometry and mechanism of the electron transfer process. Transport of the electronically neutral diazo compound from a pH-controlled hydrophilic environment to the hydrophobic environment in the heme pocket of hemoglobin, where protonation and electron transfer cause formation of a Sigma-alkyliron(III) complex of protoporphyrin IX, is expected. The existence of a crossover barrier between these environments for diazo compounds, analogous to that suggested for arenediazonium salts, will be investigated with the aid of model systems. Sensitive radical trapping experiments involving radical addition reactions will be employed to determine the chemical events that occur after the electron transfer step. The chemical reactions and reactivities of anticipated Sigma-alkyliron(III) complexes as well as the interactions of aliphatic diazonium ions with representative hemoproteins, hemerythrin, and copper proteins will be investigated.